This invention refers to a method for grinding at least one surface on a cutting blade used in machining, with a grinding wheel that rotates around an axis and that has a working area consisting of an annular surface to an advantageous use of said method; and to a grinding wheel used to carry out said method.
There are currently two techniques for grinding cutting blades used in machining, namely form grinding and generating grinding. The main difference between these two grinding techniques is that in form grinding the generatrix is produced on the tool in advance (dressing). In this manner a simple process is created in which the grinding tool carries the profile. Only one feed motion is then required to form a surface. Contrary to this, in generating grinding the generatrix is produced by at least two machine motions, which complicates the process. However, generating grinding is more flexible than form grinding, since a variety of profiles can be produced by any combinations of movement. The increased flexibility is highly desirable if small or medium-sized batches of special profiles have to be produced. In this case it is not necessary to dress the generating profile into the grinding wheel. However, generating grinding requires more elaborate control than form grinding.
A method of the above-given type is known from U.S. Pat. No. 5,168,661. In this known method a special grinding wheel configuration and a particular sequence of motions are utilized in moving the cutting blade relative to the grinding wheel, to enable the formation of a plurality of desired surfaces on a cutting blade. Furthermore, spiral-shaped furrows produced on the workpiece surface by the grain protruding highest from the grinding wheel are to be avoided. For this purpose, the known method utilizes a profile grinding wheel which is described and illustrated in the aforementioned U.S. Pat. No. 5,168,661, but which is claimed in U.S. Pat. No. 5,241,794. This known profile grinding wheel has a grinding profile which for finish grinding has a narrow, substantially flat surface on the outer portion of the wheel surface. This flat surface is kept substantially tangent to a workpiece surface during finish grinding. This profile grinding wheel consists of an expensive, highly durable abrasive material such as CBN crystals. However, other materials such as aluminum oxide can also be used, since the profile grinding wheel does not need to be dressed. Aside from the narrow, flat surface used for finish grinding, the working area of the known profile grinding wheel has an inner conical surface, an inner arcuate surface and an outer arcuate surface. The inner conical surface, the inner arcuate surface and/or the outer arcuate surface is/are used for rough grinding. The roughed blade surface is subsequently finished with the narrow flat surface.
This known method requires a complex sequence of movements, since every surface to be ground on the cutting blade is first roughed at least with the inner conical surface and subsequently finished with the narrow flat surface. The profile grinding wheel utilized in the known method comprises materials with different grain sizes in their rough grinding and finish grinding areas. The roughing and finishing work to be performed by the known profile grinding wheel is thus distributed over two different grinding wheel areas, of which the one area is used only for rough grinding and the other only for finish grinding. The cutting blades ground with the known method are common high-speed steel blades. A further disadvantage of the known method is that it is not possible to finish grind concave surfaces, since the finish grinding is always performed with the narrow flat surface. Another disadvantage of the known generating grinding method is that because of the CBN wheels employed in this method, cemented carbide blades can not be ground. A CBN wheel would not be adequately stable for machining cemented carbide blades. However, cemented carbide blades can not easily be form ground either. A broad diamond wheel would be necessary to form grind cemented carbide blades. However, such diamond wheels are very difficult to condition.
For example, to produce the teeth of a gear it can be necessary to use six different types of blades in order to produce six different profiles. These six profiles could be produced on a borazon grinding wheel by reprofiling. This would not be economical on a diamond grinding wheel. Instead, several different diamond wheels would have to be provided for the form grinding.
The object of the invention is to provide a method of the type given above, having a simpler machining cycle and enabling use of a more simply configured grinding wheel, and particularly permitting grinding to be performed on curved surfaces as well. Furthermore, an advantageous use of the method and a grinding wheel for carrying out said method are to be provided.
Contrary to the known method using a grinding wheel with a complex configuration, in the method according to the invention a universal grinding wheel can be used which has a working area consisting of an annular surface, the axial cross section of which has an arcuate profile. With the method according to the invention a surface is first generated on the cutting blade by grinding with the annular surface during a first orientation in space between the grinding wheel and the cutting blade by means of at least one first relative translational movement between the grinding wheel and the cutting blade, and then at least one part of the generated surface is reground with the annular surface during a second orientation in space between the grinding wheel and the cutting blade by means of at least one second relative translational movement between the grinding wheel and the cutting blade. According to the invention, in this manner a surface can be ground with one area of the annular surface, and it can then be reground with another area of the annular surface. The grinding wheel utilized in the method of the invention does not have to have different specifications for this in these two areas. This is because the same surface of the cutting blade can be ground and subsequently reground, that is roughed and finished, for example, solely through selection of the appropriate parameters together with the two different spatial orientations. This is true irrespective of whether the completed surface is planar, convex or concave. The grinding wheel used in the method of the invention needs only one radius in its working area, and it therefore has a substantially more simple configuration than the grinding wheel used in the known method. The process in the method according to the invention is likewise substantially simpler than in the known method, since just two different spatial orientations can be selected, for example by choosing a different angle for the cutting blade in relation to the grinding wheel. Thus, the method according to the invention is far more flexible in use than the known method. The spiral-shaped furrows, which are avoided in the known method by complicated means, are also avoided by the method according to the invention, without the necessity of using a grinding wheel with a narrow flat surface for the finish grinding.
It is possible to generate cemented carbide blades using the present invention. This is a very significant application of the method according to the invention, since dry milling, in which cutting blades of cemented carbide have to be used, is becoming increasingly common in gear production. Cemented carbide can only be machined with diamond, but diamond profile grinding wheels can hardly be profiled by dressing. Therefore, profile grinding of cemented carbide blades is virtually ruled out. Thus, simply by utilization of a diamond grinding wheel, the method according to the invention can be implemented not only for the generating grinding of cutting blades of high-speed steel, but also for that of cemented carbide cutting blades.
According to the invention, the grinding wheel used to carry out the method has a working area similar to the one provided on a grinding wheel from U.S. Pat. No. 5,259,148, which is provided for the generating grinding of glass lenses. The use of such a diamond cup-type grinding wheel with a working area located partly in a face area and partly in a cylinder area of the cup-type grinding wheel offers the advantage that planar or curved surfaces can be ground (with the face area) or alternatively concave surfaces can be ground (with the cylinder area or the face area on cutting blade used in machining), depending on the spatial orientation between the grinding wheel and the cutting blade. The wear performance improves with a diamond grinding wheel and the wheel geometry becomes more stable than in the known CBN profile grinding wheel. The diameter of the so-called profiling point, which can be precisely determined, no longer changes during a technological phase as compared to a CBN profile grinding wheel. Therefore, it is not necessary to compensate the position of the diamond grinding wheel. Furthermore, a blade shoulder with a larger over measure can be produced in a separate technological phase, thus contributing to increased economic feasibility of the process.
Since in the grinding wheel according to the invention, the working area consists of an annular surface having an arcuate profile in axial cross section which extends across a total contact angle, the roughing and finishing work areas of the grinding wheel can be displaced relative to one another or even separated within this working area by selection of different profile tilting angles. Due to the total contact angle of approximately 145xc2x0, the part of the working area being used can be selected in the face area and/or the cylinder area of the grinding wheel. Due to the circular arc profile provided in the grinding wheel according to the invention, with a radius of curvature lying within a range of 0.5 to 5 mm and preferably from 0.5 to 1 mm, and most preferably 0.5 mm or less, possibilities for flexibility in the machining of the cutting blade are offered
The cutting blades to be ground using the method according to the invention can consist of different types of cemented carbide.
A blade flank generated with the grinding wheel according to the invention can comprise one or more geometric surfaces. The surface and flank shape is produced by the relative positioning of the grinding wheel and the cutting blade. In this sense the cylinder area of the grinding wheel generates a concave surface, whereas the face area can generate a curved or a planar surface. Therefore, the blade flank can comprise two or more than two different surfaces (for instance a concave surface with a larger relief angle, and a planar facet with a smaller relief angle).
In an advantageous embodiment of the method according to the invention, the first orientation in space between the grinding wheel and the cutting blade is obtained by setting a first position of the cutting blade in relation to the grinding wheel, and the second orientation in space between the grinding wheel and the cutting blade is obtained by setting a second position of the cutting blade in relation to the grinding wheel. In this case, a conventional grinding machine can be used in which the grinding wheel is rotatable around its own axis and is movable in the Y-axis.
In another advantageous embodiment of the invention, the first position of the cutting blade is selected such that the grinding wheel generates the surface on the cutting blade with a first surface element of the annular surface located in a cylinder area of the grinding wheel, and the second position of the cutting blade is selected such that the grinding wheel grinds the at least one part of the surface generated on the cutting blade with a second surface element of the annular surface located in a face area of the grinding surface. In this case, the concave surface generated with the cylinder area can alternatively be reground with the face area in such a manner that the generated surface remains concave or becomes planar or at least partly planar.
In a further advantageous embodiment of the invention, the second position of the cutting blade is selected such that the grinding wheel generates the at least one part of the surface generated on the cutting blade as a concave or planar facet. In this case, only the spatial orientation between the grinding wheel and the cutting blade needs to be selected accordingly.
In an additional advantageous embodiment according to the invention, the stock removal during generation of a surface on the cutting blade occurs only through infeed in a Y-axis of the machine. In this case, the generating grinding process can be easily controlled.
In another advantageous embodiment according to the invention, the surface on the cutting blade is generated only with three mutually orthogonal linear axes, and other axes are utilized merely as adjustment axes and are positioned prior to the actual generating grinding of the surface on the cutting blade. In this case, every desired surface can be generated on the cutting blade with three controlled linear movements on a conventional grinding machine such as that of type B22 of the applicant (cf. the company brochure xe2x80x9cCNC-Werkzeugschleifzelle Oerlikon B22xe2x80x9d OGT-B22/D/hJ) or type B5 of the applicant (cf. the two company brochures, both entitled xe2x80x9cprofil B5xe2x80x9d, sections 1.11-d/e-cH and OGT-profil B5/E/dH, respectively).
In a further advantageous embodiment according to the invention, the surface on the cutting blade is generated in the one and/or the other step in two operations by means of two first and two second relative translational movements between the grinding wheel and the cutting blade, respectively. In this case, the surface can be roughed and finished in two steps each.
In an additional advantageous embodiment according to the invention, the method is carried out on a CNC machine. In this case, the grinding process can be controlled in a conventional manner with regard to the geometry and the technology.
In another advantageous embodiment according to the invention, a CDS computer system (CDS is the abbreviation of Controlled Disk System) is used to determine interrelations between geometric and technological parameters for the generating grinding. In this case, a special software package is all that is required to convert a conventional grinding machine, such as the aforementioned type B22, to the generating grinding according to the invention.
In another advantageous embodiment according to the invention, the surface on the cutting blade is generated in the one step with at least one roughing cut, and the at least one part of the generated surface is reground with a finishing cut in the other step. In this case, each surface can be generated separately and the macro and micro surface geometries can be separately influenced.
In another advantageous embodiment according to the invention, the relative translational movement between the grinding wheel and the cutting blade is produced by imparting a thrust or pulling motion to the cutting blade relative to the grinding wheel. In this case, the desired simple machining cycle can be achieved by the corresponding selection of this motion.
In another advantageous embodiment according to the invention, a pulling motion relative to the grinding wheel is imparted to the cutting blade during regrinding with a finishing cut. Although this is preferred, a thrust motion can be advantageous for the finishing cut instead of the pulling motion, depending on the surface to be ground. Each technological phase (roughing or finishing) can be separately defined geometrically and technologically in the advantageous embodiments of the method according to the invention.
In another advantageous embodiment according to the invention, a grinding wheel is used which has the same specifications over its entire annular surface used for grinding. In this case, it is advantageous to select the roughing cut and the finishing cut solely through selection of feed parameters such as direction and rate of feed.
In yet another advantageous embodiment according to the invention, roughing and finishing are interchangeable in the two steps of the method according to the invention and, therefore, so are the surface elements of the annular surface used for grinding. To be sure, two technological phases, roughing and finishing, could be required. However, the technological process can include a plurality of roughing cuts and one finishing cut and vice versa.
In another advantageous embodiment of the grinding wheel according to the invention, the grinding wheel has a fixed geometry and can not be dressed. This makes its production especially simple. It is far easier to perform grinding with only one specific radius if the radius is kept constant. This is the case with diamond grinding wheels, which have a long service life. It can be assumed that the method is carried out with a constant radius, which simplifies and facilitates the process control. The question of whether a dressable or nondressable grinding wheel is used depends on the grinding capacity of the grinding wheel.
A nondressable grinding wheel preferably comprises a metallic carrier body onto which an abrasive coating of diamond grit and a galvanic bonding from which the diamond grit protrudes is applied, with the galvanic bonding preferably consisting of nickel.
A dressable grinding wheel can be used instead of a nondressable grinding wheel. That is quite possible due to the design of the type B22 machine, since it has a suitable dressing means, and suitable dressing software is provided to permit occasional dressing of the grinding wheel in order to reprofile its radius.